Cathode assembly for indirectly heated cathode ion source

Abstract

A cathode in an indirectly heated cathode ion source is supported by at least one rod or pin. The cathode is preferably in the form of a disk, and the support rod is smaller in diameter than the disk to limit thermal conduction and radiation. In one embodiment, the cathode is supported by a single rod at or near its center. The support rod may be held by a spring-action clamp for simple and reliable clamping and unclamping. The disk shaped cathode and the support rod may be fabricated as a single piece. A filament that emits electrons thermionically may be disposed around the rod in close proximity to the cathode.

1. A cathode sub-assembly for an ion source comprising:
 an indirectly heated cathode having an outer periphery and an interior area; and 
 a support rod being fixedly attached to the interior area of the indirectly heated cathode for supporting the cathode within an arc chamber of the ion source, the indirectly heated cathode configured to emit electrons within the arc chamber that collide with gas molecules within the arc chamber to produce ions for implantation. 
 
   
   
     2. The cathode sub-assembly as defined in  claim 1  wherein the support rod is attached to a surface of the cathode facing away from the arc chamber. 
   
   
     3. The cathode sub-assembly as defined in  claim 2  wherein the cathode is in the shape of a disk. 
   
   
     4. The cathode sub-assembly as defined in  claim 3  wherein the support rod is fixedly attached at or near the center of the cathode, along an axis of the cathode. 
   
   
     5. The cathode sub-assembly as defined in  claim 4  wherein the support rod is in the shape of a cylinder and the diameter of the cathode is larger than a diameter of the support rod. 
   
   
     6. The cathode sub-assembly as defined in  claim 5  wherein the diameter of the cathode is at least four times larger than the diameter of the support rod. 
   
   
     7. The cathode sub-assembly as defined in  claim 5  further comprising a spring loaded clamp for holding the support rod. 
   
   
     8. The cathode sub-assembly as defined in  claim 1  wherein the support rod mechanically supports and conducts electrical energy to the cathode. 
   
   
     9. The cathode sub-assembly as defined in  claim 1  wherein the support rod is press fitted to the indirectly heated cathode. 
   
   
     10. The cathode sub-assembly as defined in  claim 1 , further comprising a filament configured to emit electrons, wherein the support comprises a first surface having an edge directly coupled to the indirectly heated cathode, and wherein the filament is disposed around the first surface in close proximity to the cathode. 
   
   
     11. A cathode assembly for use in an indirectly heated cathode ion source which includes an arc chamber housing that defines an arc chamber, comprising:
 a cathode sub-assembly including a cathode and a support rod, the cathode having an outer periphery and an interior area, the support rod being fixedly mounted to the interior area of the cathode, and the cathode being configured to mit elections within the arc chamber that collide with gas molecules within the arc chamber to produce ions for implantation; and 
 a filament configured to emit electrons, the filament being positioned outside the arc chamber in close proximity to the support rod of the cathode sub-assembly. 
 
   
   
     12. The cathode assembly as defined in  claim 11  wherein the filament is disposed around the support rod in close proximity to the cathode and isolated from a plasma in the arc chamber. 
   
   
     13. The cathode assembly as defined in  claim 11  wherein the filament is disposed around the support rod in close proximity to the cathode and isolated from a plasma in the arc chamber, wherein the filament is fabricated of an electrically conductive material and includes an arc-shaped turn having an inside diameter greater than or equal to the diameter of the support rod. 
   
   
     14. The cathode assembly as defined in  claim 11 , further comprising a cathode insulator disposed around the cathode of the cathode sub-assembly, wherein the cathode insulator is configured to electrically and thermally isolate the cathode from the arc chamber housing. 
   
   
     15. The cathode assembly as defined in  claim 14 , wherein said cathode insulator includes an opening having a diameter that is larger than or equal to the diameter of the cathode. 
   
   
     16. The cathode assembly as defined in  claim 15  wherein a vacuum gap is provided between the cathode insulator and the cathode to limit thermal conduction. 
   
   
     17. The cathode assembly of  claim 15  wherein said cathode insulator has a generally tubular shape with a sidewall and includes a flange, for shielding the sidewall of the cathode insulator from a plasma in the arc chamber. 
   
   
     18. The cathode assembly of  claim 17  wherein said flange is provided with a groove on a side of the flange facing away from the plasma, for increasing a path length between the cathode and the arc chamber housing. 
   
   
     19. The cathode assembly as defined in  claim 11  wherein the support rod is press fitted to the cathode. 
   
   
     20. A cathode assembly for use in an indirectly heated cathode ion source which includes an arc chamber housing that defines an arc chamber, comprising:
 a cathode sub-assembly including a cathode and a support rod, the cathode having an outer periphery and an interior area, the support rod fixedly mounted to the interior area of the cathode, the cathode configured to emit electrons within the arc chamber that collide with gas molecules within the arc chamber to produce ions for implantation; and 
 a filament configured to emit electrons, the filament being positioned outside the arc chamber in close proximity to the support rod of the cathode sub-assembly, 
 wherein the filament is disposed around the support rod in close proximity to the cathode and isolated from a plasma in the arc chamber, wherein the filament is fabricated of an electrically conductive material and includes an arc-shaped turn having an inside diameter greater than or equal to the diameter of the support rod, and wherein a cross-sectional area of the filament varies along a length of the filament, and is smallest along the arc-shaped turn. 
 
   
   
     21. The cathode assembly as defined in  claim 20  wherein the support rod is press fitted to the cathode. 
   
   
     22. A method for supporting and indirectly heating a cathode of an ion source comprising:
 supporting the cathode having an outer periphery and an interior area by a rod fixedly attached to the interior area of the cathode; 
 bombarding the cathode with electrons from a filament positioned outside an arc chamber of the ion source for heating of the cathode; and 
 emitting electrons from the cathode for collision with gas molecules within the arc chamber to produce ions for implantation. 
 
   
   
     23. The method as defined in  claim 22  wherein the step of supporting comprises press fitting the rod to the cathode. 
   
   
     24. A cathode assembly for an ion source comprising:
 a cathode having an outer periphery and an interior area; 
 a support rod fixedly attached to the interior area of the cathode; and 
 an indirect heating device for indirectly heating the cathode, wherein the cathode is configured to emit electrons within an arc chamber of the ion source that collide with gas molecules within the arc chamber to produce ions for implantation in response to the heating of the cathode. 
 
   
   
     25. The cathode assembly as defined in  claim 24  wherein the support rod is press fitted to the cathode.